Loom control system

ABSTRACT

The present invention relates to a loom control system operable to stop a loom in the presence of a yarn breakage. This loom comprises a feeding device having a yarn storage drum for temporarily storing the yarn and a yarn store sensor for sensing the quantity of yarn stored on the drum of the feeding device and for transmitting an electric sensor signal representing the quantity of yarn stored on the drum to the feeding device to control the operation of the feeding device and to thereby control the quantity of yarn stored on the drum. A monitor circuit is electrically connected to the yarn store sensor for receiving the sensor signal, wherein the monitor circuit derives information on yarn breakage before and/or after the feeding device from the sensor signal or its variation with respect to time to generate a stop signal for the loom.

FIELD OF THE INVENTION

The present invention relates to a loom control system and, inparticular, to a loom control system operable to stop a loom in thepresence of a yarn breakage, the loom including a feeding device havinga yarn storage drum for temporarily storing the yarn and including ayarn store sensor for sensing the quantity of yarn stored on the drum ofthe feeding device and for transmitting an electric sensor signalrepresenting the quantity of yarn stored on the drum to the feedingdevice to control the operation of the feeding device in a mannercontrolling the quantity of yarn stored on the drum, the loom controlsystem including a monitor arrangement for stopping the loom in responseto a yarn breakage.

BACKGROUND OF THE INVENTION

A loom control system comprising these features is already known fromU.S. Pat. No. 4,326,564. In the art of weaving it is well known toprovide an automatic loom with a loom control system operable to stopthe loom in the presence of a yarn breakage. Automatic looms comprise afeeding device having a yarn storage drum for temporarily storing theyarn. Such feeding devices eliminate the wide variations in yarn tensionwhich occur when a yarn is delivered from a supply source, and permitthe yarn to be fed to the loom at a substantially constant tension,although the yarn is intermittently fed from the feeding device to theloom. Typically, such feeding device may either have a yarn storage drumupon which the yarn is wound as the drum is driven by an electric motoror the feeding device may incorporate a stationary yarn storage drumwith an orbiting feeder tube driven by an electric motor and engagingthe weft yarn to apply it to the surface of the stationary yarn storagedrum. The feeding device includes a yarn store sensor which senses thequantity of yarn stored on the drum of the feeding device. The yarnstore sensor generates an electric sensor signal representing saidquantity of yarn. This signal is used for controlling the operation ofthe feeding device so as to control the quantity of yarn stored on thedrum. Particularly, the sensor signal might be fed to a control unitwhich controls the operation of the feeding device by increasing ordecreasing the rotary speed of the motor of the feeding device in such amanner so that the quantity of yarn stored on the drum essentiallyremains between a maximum quantity and a minimum quantity of yarn.

It is also known from the above-mentioned U.S. patent to equip loomcontrol systems of the above-mentioned kind with a monitor means forstopping the loom in the presence of a yarn breakage. Such monitor meansis necessary, as the weft yarn being conveyed from the yarn supply spoolto the feeding device might break, which results in the weft yarn storedon the yarn storage drum ultimately becoming exhausted if the loomcontinues to operate. In that event, the insertion of the broken yarnwill produce a defect in the woven fabric. Thus, it is desirable to stopthe operation of the loom in case of a yarn breakage. The prior artmonitor means comprise a tension device arranged between the yarn supplyspool and the feeding device for sensing the yarn tension. The tensiondevice generates a signal having a high logical potential if the yarntension is above a predetermined value. If there is no yarn breakage,the output signal of the tension device is "high" during the feedingoperation of the feeding device. If contrary hereto there occurs a yarnbreakage between the yarn supply spool and the yarn storage feeder, theoutput signal of the tension device changes to zero potential. Thus, theoccurence of a zero-signal during the operation of the feeding device isindicative of a yarn breakage, so that the simultaneous occurence ofthis zero-tension signal and a signal indicating the feeding deviceoperation can be used for stopping the loom.

However, a yarn breakage might also occur between the yarn storagefeeder and the loom. The prior art loom control system can onlyrecognise this second kind of yarn breakage if it is equipped with asecond tension device between the feeding device and the loom.Therefore, the prior art loom control system is undesirably complicatedif arranged such that it is responsive to a yarn breakage before andafter the feeding device. Furthermore, the prior art loom control systemis not adapted to stop the loom in case of a malfunction of the feedingdevice, said malfunction either resulting in the case where the quantityof yarn stored on the drum exceeds a maximum quantity or resulting inthe contrary case where the quantity of yarn falls below a predeterminedminimum quantity. It is considered as being a further drawback of thisprior art loom control system that its tension devices only have a quiteunreliable operation as they are highly sensitive to dirt and dust whichcan prevent a correct operation of the tension device. Particularly, thefree movability of the mechanically movable parts of the tension devicecan be blocked by dirt or dust. In addition, considerable wear occursbetween yarn guiding eyelets of the tension device and the yarn. Thewear increases in the case of an accumulation of dirt at the eyelets.

The task underlying the invention is to provide a loom control system inaccordance with the generic clause of the main claim, which has a simpleand cost-saving structure and which is reliable in operation.

SUMMARY OF THE INVENTION

This technical problem is solved by a loom control system which is basedon the principal idea that information on yarn breakage is directlyderivable from a sensor signal representing the quantity of yarn storedon a yarn storage drum or from the sensor signal variation with respectto time. In other words, the yarn store sensor which is used in priorart loom control systems only for controlling the feeding operation ofthe feeding device is also used as a yarn breakage detector by beingconnected to a monitor means deriving information on yarn breakagebefore and/or after the feeding device from said sensor signal or itsvariation with respect to time. Thus, complicated, costly and unreliableadditional yarn breakage sensors, like tension devices, as they are usedin prior art loom control systems, are superfluous in the loom controlsystem according to the present invention. Thus, the present inventionprovides a cost-saving, simple and reliable loom control system. Anadditional advantage of the present loom control system consists in thatit is capable of detecting a malfunction of the feeding device or of acontrol unit for controlling the feeding operation of the feedingdevice, and that it is further capable of stopping the loom in case of amalfunction of the feeding device. An additional advantage of the loomcontrol system in accordance with the present invention is that itavoids a problem of prior art loom control systems regarding thearrangement of a yarn breakage sensor in the narrow space between a yarnsupply means and the feeding device.

When carrying out the invention according to one form of the invention,the most simple kind of yarn store sensors can be used, namely aso-called digital yarn store sensor generating a sensor signalindicating whether or not the quantity of stored yarn is below a minimumthreshold. Under normal operation conditions, i.e. if there is no yarnbreakage before the feeding device, the quantity of yarn stored on thedrum only passes below a minimum threshold during a very short period oftime, as in this case the feeding device is controlled to increase thequantity of yarn stored on the drum. If contrary hereto a yarn breakageoccurs before the feeding device, the quantity of yarn stored on thedrum runs and remains below the minimum quantity or below the minimumthreshold as no yarn can be fed to the drum even by accelerating thefeeding device operation. The monitor means comprises a time circuitresponsive to a lapse of time during which the sensor signal indicatesthat the quantity of stored yarn is continuously below this minimumthreshold. If this lapsed time exceeds a predetermined time threshold,which clearly indicates a yarn breakage before the feeding device, themonitor means stops the operation of the loom.

A loom control system according to a further form of the invention canbe used for controlling the operation of a loom which is equipped with afeeding device of the kind which is controlled to essentiallycontinuously feed the yarn to the drum. Under normal operatingconditions, that means if no yarn breakage occurs before the feedingdevice, the quantity of yarn stored on the drum continuously increasesdue to the feeding device operation, if no yarn is withdrawn by the loomfrom the drum, and continuously decreases, if a withdrawal of yarn fromthe drum takes place. During the latter condition, this means duringwithdrawal of yarn from the drum the time-dependent quantity of storedyarn has a predetermined negative gradient, wherein this negativegradient corresponds to the quantity of yarn fed to the drum by means ofthe feeding device per time unit, diminished by the quantity of yarnwithdrawn from the drum per time unit. If a yarn breakage occurs beforethe feeding device, said negative gradient becomes more negative thanthe above mentioned one due to the fact that the quantity of yarn fed tothe drum by means of the feeding device becomes zero in case of a yarnbreakage.

Thus, information on yarn breakage can be derived from the absolutevalue of said negative gradient of the quantity of stored yarn withrespect to the time. The above-mentioned yarn breakage detection iscarried out by a loom control system according to the invention and isconsidered as being highly advantageous as it stops the loom operationwithout any essential time delay between the occurence of a yarnbreakage and the stopping of the loom. In other words, the loom controlsystem is capable of detecting a yarn breakage without any time circuitsand thus operates extremely fast.

A further form of the invention relates to a loom control system whichis a modification of the system just discussed and which is also adaptedfor, but not limited to, controlling a loom which is equipped with afeeding device having a so-called on-and-off-operation. In other words,the loom control system can also be used for a loom, the feeding deviceof which is not controlled to essentially continuously feed the yarn tothe drum. Under normal operation conditions of the loom, if no yarnbreakage occurs before the feeding device, the quantity of stored yarnonly decreases during a certain period of time until reaching a lower orminimum threshold, and then increases due to the feeding deviceoperation. If there is a yarn breakage before the feeding device, thegradient of the sensor signal as generated by the yarn store sensorremains negative as no yarn is fed to the drum. Therefore, it ispossible to derive information on yarn breakage in response to a lapseof time during which said gradient is continuously negative.

When carrying out the invention according to another form thereof, theloom control system is capable of detecting a yarn breakage between thefeeding device and the loom. Under normal operational conditions (ifthere is no yarn breakage between the feeding device and the loom), aweft yarn insertion in the loom results in a decreasing quantity of yarnstored on the drum and therefore in a negative gradient of the quantityof stored yarn with respect to time. When the weft yarn insertion iscompleted or when no further weft yarn insertion takes place, thewithdrawal of the yarn from the drum will also come to an end but with acertain time delay relative to the weft yarn insertion operation,wherein this time delay is caused by a slack in the yarn between thefeeding device and the loom and by the elasticity of the yarn itself.Thus, the gradient of the quantity of yarn stored on the drum willbecome positive a certain period of time after completing the weft yarninsertion. If there is a yarn breakage, the gradient of the quantity ofyarn stored on the drum will not change from a negative gradient to azero gradient or a positive gradient. Thus, information on yarn breakagecan be derived by detecting whether or not the gradient of the quantityof yarn changes from a negative gradient to a zero or positive gradientwithin a predetermined period of time after completing the weft yarninsertion. Thus, the monitor means stops the loom if the above mentionedcondition is not fulfilled, which indicates that a yarn breakage betweenthe feeding device and the loom has occurred.

A further advantageous embodiment of the present invention includes aloom control system which can be used for a loom equipped with a feedingdevice which is controlled to essentially continuously feed the yarn tothe drum. The loom control system is adapted to stop the operation ofthe loom if a yarn breakage occurs between the feeding device and theloom. Under normal operational conditions, where no yarn breakage occursbetween the feeding device and the loom, the quantity of yarn stored onthe drum decreases during weft yarn insertion in the loom. In otherwords, the gradient of the quantity of stored yarn is negative duringweft yarn insertion, although the feeding drum feeds yarn to the drum atall times. If the yarn breaks between the feeding device and the loom,no yarn is withdrawn from the drum during weft yarn insertion. Thus, thequantity of yarn stored on the drum increases even during the insertingof the loom. Consequently, a positive gradient of the quantity of storedyarn with respect to time during weft yarn insertion can be used forderiving information on yarn breakage between the feeding device and theloom. The loom control system operates without any essential time delaybetween the occurence of yarn breakage and the stopping of the loom, asthis system does not require any time circuit for detecting the yarnbreakage.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, preferred embodiments of the present invention aredescribed with reference to the accompanying drawings, wherein:

FIG. 1 shows a cross section through a feeding device having a yarnstore sensor, and a loom control system connected thereto;

FIG. 2 shows an enlarged view of the yarn store sensor and itsarrangment with respect to a storage drum of the feeding device of FIG.1;

FIGS. 3 and 4 are an illustration for explaining the mode of operationof a digital yarn store sensor;

FIG. 5 is a system block diagram of a first embodiment of the presentinvention;

FIG. 6 is a circuit diagram of the first embodiment of FIG. 5;

FIG. 7 is a system block diagram of a second embodiment of the presentinvention;

FIG. 8 is a system block diagram of a third embodiment of the presentinvention;

FIG. 9 is a system diagram of a fourth embodiment of the presentinvention;

FIG. 10 is a circuit diagram of the fourth embodiment as shown in FIG.9; and

FIG. 11 is a fifth embodiment of the present invention.

DETAILED DESCRIPTION

As shown in FIG. 1, a feeding device 1 of a loom or weaving machinecomprises a yarn storage drum 2, an electric motor 3 and an orbitingfeeder tube 4. The yarn storage drum 2 is rotatably connected to a shaftof the electric motor and is maintained in a stationary position withrespect to its environment by a magnetic means (not shown here). Theorbiting feeder tube 4 has an inner bore guiding the yarn F from asupply spool S to an outer circumferential surface of the yarn storagedrum 2. The orbiting feeder tube 4 is driven by the electric motor 3.For purposes of the present disclosure, reference will be made to theso-called stationary drum feeding devices, wherein this art isexemplified by U.S. Pat. No. 3,776,480 and by U.S. Pat. No. 3,853,153.It should be noted that the present invention has equal application toso-called rotary drum feeding devices.

The yarn is withdrawn from the yarn storage drum 2 through a withdrawaleyelet 5 to the loom or to the weaving machine (not shown here). Asshown in FIG. 1, and in more detail in FIG. 2, the feeding device isprovided with a yarn store sensor 6-9. In the shown embodiment, the yarnstore sensor consists of a so-called minimum sensor 6 and 7 and aso-called maximum sensor 8,9. Each of these sensors comprise arespective light emitting device 6,8 and a light sensing device 7,9. Thedetailed operation of these sensors will be explained with reference toFIGS. 3 and 4. The respective sensors are arranged so as to opposepredetermined axial locations at the surface of the yarn storage drum 2corresponding to a predetermined maximum quantity of stored yarn or apredetermined minimum quantity of stored yarn, respectively. The outputsignals of the respective light sensing devices 7,9 of the minimumsensor or the maximum sensor are fed to a control unit 11 forcontrolling the operation of the electric motor 3 so as to therebycontrol the momentary quantity of yarn stored on the storage drum 2.Control units for properly controlling the speed of the motor 3 are wellknown in the art. This art is exemplified by the Swedish Pat. No. 77 12808 (applicant's own).

A monitor means 10 is electrically connected to the yarn store sensor6-9 for receiving the sensor output signal. The monitor means 10 isresponsive to the sensor signal and, in particular derives informationon yarn breakage before and/or after the feeding device 1 from saidsensor signal or its variation with respect to time to generate a stopsignal for the loom in case of a yarn breakage or to interrupt the powersupply line of the loom. The generated stop signal for the loom can alsobe used for opening a feeder device stop switch 12 which electricallyconnects the electric motor 3 with the control unit 11. Thus, in case ofa yarn breakage, the monitor means 10 stops the operation of the loomand the feeding device.

Referring now to FIGS. 2 to 4, the mode of operation of a so-calledminimum sensor will be explained. The light emitting device 6, whichmight be a conventional light emitting diode supplied with a DC-voltage,generates a light beam, which is directed to a light-reflecting surfaceof the yarn storage drum 2. If there is no yarn at the location of thedrum surface opposing said light emitting device 6, the incoming lightwill be reflected by the surface. Otherwise, no light reflection takesplace, that means which the energy of incoming light is attenuated bythe yarn. A light sensing device 7, which might be a light-sensitivetransistor 7, is located near the light emitting device 6 so as toreceive the reflected light energy. Thus, an optical minimum or maximumsensor, as known per se in the art, can be realized.

Referring now to FIG. 5, a first embodiment of the loom control systemin accordance with the present invention comprises a digital yarn storesensor 20, a low pass filter 21, an inverter 22, an integrating circuit23, a threshold comparator 24, a RS-flip-flop circuit 25, and a relay26. The digital yarn store sensor 20 generates a sensor signalindicating whether or not the quantity of stored yarn is below a minimumthreshold. This yarn store sensor can comprise a light emitting device 6and a light sensing device 7, as shown in FIGS. 1 to 4. Said sensorsignal has a high logical potential if the quantity of stored yarn isbelow a minimum threshold. Said sensor signal has a noise component,which is attenuated by the low pass filter 21 connected to the sensor20. The inverter 22 is connected to the output of the low pass filter 21for inverting the logical value of the output signal of the low passfilter. The inverter output signal has a low logical potential if thesensor signal indicates that the quantity of stored yarn is below aminimum threshold. The inverter output signal 22 is fed to areset-terminal of an integrating circuit 23. The integrating circuit 23generates a continuously increasing output signal when it is not resetby a high logical potential reset signal fed to its input. Otherwise,the integrating circuit 23 has a zero voltage output signal. Thethreshold comparator 24 compares the output signal of the integratingcircuit 23 with a predetermined voltage threshold. If its input signalexceeds the voltage threshold, the comparator 24 transmitts a highlogical potential. Otherwise, the threshold comparator 24 generates azero voltage output signal. The output of the threshold comparator 24 iselectrically connected to the set-terminal of the RS-flip-flop circuit25. This circuit 25 is set by a high signal as received from thethreshold comparator. It remains in its set-condition until it is resetby feeding a high potential signal to its reset terminal. A power-relayis connected to the output of circuit 25. The relay interrupts the loompower supply line, if a high logical potential is fed to its inputterminal.

Hereinafter, the mode of operation of the embodiment as shown in FIG. 5will be explained. Under normal operational conditions, where no yarnbreakage occurs between the feeding device 1 and the supply spool S, theoutput signal of the digital yarn store sensor 20 generally remains atlow logical potential. However, even under said conditions, the yarnstore sensor 20 periodically generates pulses of high logical potentialdue to the fact that there is a time delay caused by the response-timeof the electric motor 3 between the detection of a minimum quantity ofstored yarn on the drum 2 and the acceleration of the electric motor 3as controlled by control unit 11. Thus, the output signal of the digitalyarn store sensor 20 will be generally at low logical potential, butsometimes changes to a high logical potential for a quite short periodof time. Higher harmonic frequencies of this output signal are supressedin the low pass filter 21. The integrating circuit remains in itsreset-condition when the output signal of sensor 20 is at low logicalpotential and carries out a short-time integration during the sensorsignal high condition. Thus, the output signal of the integratingcircuit 23 remains at low logical potential or continuously rises fromzero volts to a relatively low voltage. The threshold comparator 24compares this signal with a predetermined voltage threshold. Thisvoltage threshold is adjusted such as to be higher than the highestoutput signal of the integrating circuit 23 under normal operatingconditions of the loom. Thus, the output signal of threshold comparator24 remains at zero potential if the comparator is supplied with theabove mentioned output signal of the integrating circuit 23. Thus, theRS-flip-flop circuit 25 remains in its reset condition and thereforefeeds a low logical potential signal to the relay 26. The relay 26 is ofthe normally closed type, which means that its power switch is in anormally closed condition. One terminal of the relay power switch isconnected to the mains, whereas the other output terminal is connectedto a loom power supply input terminal. Hence, the loom is supplied withan AC-current if no yarn breakage is detected by the digital yarn storesensor 20.

In case a yarn breakage occurs between the supply spool S and thefeeding device 1, the quantity of yarn on the drum 2 will decrease andwill cause the digital yarn store sensor 20 to produce a high logicalpotential signal. Thus, the input signal of the integrating circuit 23changes to low logical potential as soon as a yarn breakage is detected.Therefore, a continuously increasing voltage signal appears at theoutput terminal of the integrating circuit 23. As soon as this voltageexceeds the threshold voltage of the threshold comparator 24, thecomparator 24 generates a signal having a high logical potential. Thus,the RS-flip-flop circuit 24 is set. Hence, circuit 25 feeds a highlogical potential signal to relay 26 so as to open the power switch ofthis relay. Thus, the loom becomes disconnected from the mains in caseof a yarn breakage.

Referring now to FIG. 6, there is shown a circuit diagram of theembodiment as shown in FIG. 5. The low pass filter 21 comprises aresistor R₁ and a capacitor C₁ which are serially connected, and whichdetermine a suitable transmission characteristics. The junction node ofthese elements R₁, C₁ is connected to the input terminal of inverter 22,comprising an operational amplifier OP₁ having an input resistor R₂connected to its negative terminal and a feedback-resistor R₃ in itsfeedback-path. The output of the inverter 22 is connected to the base ofa transistor T₁ which is in parallel to a capacitor C₂ which in turn isserially connected to a DC-source having a predetermined voltage V bymeans of a further resistor R₅. The common node of the resistor R₅ andC₂ is connected to the input terminal of a threshold comparator 24. Thiscomparator 24 consists of an operational amplifier OP₂ and a voltagedividing variable resistor R₄, which is connected with its end to theabove-mentioned DC-source, with its other end to the ground and with itsintermediate terminal to the negative terminal of the operationalamplifier OP₂. The positive input terminal of this operational amplifieris the input terminal of said comparator circuit. An output of thethreshold comparator 24 is connected to a set-terminal of a RS-flip-flopcircuit 25, whereas the reset terminal of this circuit 25 is connectableto a high logical potential V by means of a manual reset switch 27. Theoutput of this hold-circuit is connected to one input terminal of apower-relay 26, whereas its other input terminal is grounded. This relay26 comprises a normally closed switch NC.

Referring now to FIG. 7, there is shown a second embodiment of the loomcontrol system according to the present invention. This system comprisesan analog yarn store sensor 30, a low pass filter 31, a differentiatoror derivator 32, an inverter 33, a threshold comparator 34, aRS-flip-flop circuit 35 and a relay 36, these elements being seriallyconnected in this order. This embodiment is suitable for a loom having afeeding device 1 which is controlled to essentially continuously feedthe yarn to the storage drum 2. For understanding the mode of operationof this second embodiment, the time-dependency of the quantity of yarnstored on the storage drum 2 under normal conditions, i.e. if no yarnbreakage occurs between the supply spool S and the feeding device 1, andunder abnormal conditions, i.e. if a yarn breakage occurs, will beconsidered hereinafter. Under normal operating conditions, the quantityof yarn has a positive gradient during a first period of time, in whichthe feeding device 1 stores yarn on the storage drum 2 and the loom doesnot withdraw any yarn from this drum, and a predetermined negativegradient of the quantity with respect to the time during a second periodof time, during which yarn is withdrawn from the drum and during whichyarn is fed to the drum by the feeding device 1. This predeterminednegative gradient is the difference between the quantity of yarn fed tothe drum per time unit and the quantity of yarn withdrawn from the drumper time unit. If a yarn breakage occurs, the quantity of yarn fed tothe drum per time unit becomes zero, so that the gradient becomes morenegative than the predetermined one. Thus, information on yarn breakagecan be derived from the gradient of the quantity of stored yarn withrespect to time.

The analog yarn store sensor 30 is per se well known in the art, so thata detailed description of this analog yarn store sensor can be omitted.Exemplifications of such sensors are found in the Swedish Pat. No. 77 12808 (applicant's own).

The output signal of this analog yarn store sensor is proportional tothe quantity of yarn stored on the drum. This signal is smoothed by thelow pass filter 31 and fed to the derivator 32. The output signal ofthis derivator 32 corresponds to the gradient or first derivation of thequantity of stored yarn with respect to the time. The sign of thisgradient is changed by the inverter 33 from minus to plus or from plusto minus, respectively. Thus, the output signal of the inverter 33 isindirectly proportional to the gradient of the quantity of stored yarnwith respect to the time. This inverted gradient signal is fed to thethreshold comparator 34, which compares the absolute value of thisnegative gradient signal with a predetermined gradient threshold. If theabsolute value exceeds said gradient threshold, the RS-flip-flop circuit35 is set by its input signal. The output signal of this circuit 35 isfed to a relay 36 which corresponds to the relay 26 in the firstembodiment shown in FIGS. 5 and 6. Thus, the loom is stopped if thegradient of the quantity of stored yarn with respect to the time becomesmore negative than a predetermined negative value, which indicates ayarn breakage between the supply spool S and the feeding device 1.

FIG. 8 shows a third embodiment of the present invention. Identical orsimilar circuit elements are designated with the same reference numeralsas used in the foregoing Figures. As mentioned above, the quantity ofstored yarn with respect to time has a positive gradient during a firstperiod of time and a negative gradient during a second period of time,again a positive gradient during a third period of time corresponding tothe first period of time and so on. However, if a yarn breakage occursbetween the spool and the feeding device, said gradient never becomespositive. Consequently, a gradient which never becomes positiveindicates a yarn breakage.

This third embodiment comprises an analog yarn store sensor 30, a lowpass filter 31, a derivator 32, an integrating circuit 40, a thresholdcomparator 34, a RS-flip-flop circuit 35 and a relay 36, wherein thesecircuit elements are serially connected in this order. The output signalof the analog yarn store sensor 30 is fed to the low pass filter 31smoothing said signal and further fed to the derivator 32, the outputsignal of which corresponds to the first derivation or gradient of thequantity of stored yarn with respect to time. A positive gradient signalresets the integrating circuit 40. Thus, under normal operatingconditions, the integrating circuit 40 is periodically reset by thepositive gradient signal. In case of a yarn breakage, the integratingcircuit 40 receives no reset-signal. This circuit may be realizedsimilar to the integrating circuit 23 as shown in FIG. 6, but has aslower integrating operation when compared with the operation of circuit23. The output signal of the integrating circuit 40 is similar to asawtooth-wave form in case of normal operation conditions, and alwayshas an increasing voltage in case of a yarn breakage. The thresholdcomparator 34 compares this signal with a predetermined thresholdvoltage being such that the output signal of the integrating circuit 40never exceeds the threshold voltage if no yarn breakage occurs.Otherwise, the output voltage of the integrating circuit 40 continuouslyincreases (until reaching an upper limit voltage similar to the supplyvoltage of the integrating circuit 40) and thereby causes the thresholdcomparator 34 to generate a high potential output signal. This signal isfed to the set terminal of the RS-flip-flop circuit 35 which is set incase of a yarn breakage. Hence, a high logical potential signal is fedto the relay 36 in case of a yarn breakage, so that the loom operationis stopped.

An alternative fourth embodiment of the loom control system inaccordance with the present invention for stopping the loom in case of ayarn breakage between the supply spool S and the feeding device 1 isshown in FIG. 9. This embodiment comprises an analog yarn store sensor30 connected to a low pass filter 31 for smoothing the sensor outputsignal. The output signal of the low pass filter is fed to a derivator32. The output signal of the derivator 32 is fed to a first inputterminal of an OR-gate 46. The other input terminal of this gate 46 isconnected to an output terminal of a digital weft yarn insertion sensor.This weft yarn insertion sensor generates a yarn insertion signal havinga high logical potential when weft insertion takes place and having alow logical potential when no weft yarn insertion takes place. Thissensor can be realized as a switch connected to a DC-source andoperated, i.e. opened or closed by the respective position of a weftyarn insertion means (not shown here). The output signal of gate 46 isfed to a reset terminal of an integrating circuit 40, which in turn isconnected to a threshold comparator 34 comparing the output signal ofthe integrating circuit 40 with a predetermined voltage threshold. Ifthis output signal exceeds said voltage threshold, the comparatorgenerates a high logical potential output signal. Otherwise, the outputsignal of the threshold comparator 34 remains at low potential. Thissignal is fed to hold-circuit or RS-flip-flop circuit 35 which turns onor off a relay 36 wherein these elements 35,36 correspond to elements35, 36 as described with reference to the foregoing Figures.

Under normal operating conditions, the gradient of the quantity ofstored yarn with respect to time changes from a negative gradient to apositive gradient if the weft yarn insertion has come to an end, so thatthe withdrawal of yarn from the drum 2 has come to an end. However, itshould be noted that there is a time delay between the end of weft yarninsertion and the end of withdrawal of yarn from the drum, this timedelay being caused by certain machine characteristics and yarncharacteristics such as elasticity. Thus, the end of withdrawal of yarnfrom the drum is a little later than the end of weft yarn insertion.Thus, under normal operating conditions, if no yarn breakage occursbetween the supply spool and the feeding device, the gradient changesfrom negative to positive at a moment which is a little later than themoment at which the weft yarn insertion signal changes from high logicalpotential to zero logical potential. If a yarn breakage occurs, thegradient does not change from negative to positive within a period oftime corresponding to the above mentioned delay-time after the weft yarninsertion signal changed from high to low. Thus, the period of timebetween said change of the weft yarn insertion signal and said change ofgradient can be used for deriving information on yarn breakage.

The integrating circuit 40 remains in its reset condition as long as thesensor 45 generates a weft yarn insertion signal. If this signal changesto low potential, indicating that the weft yarn insertion has come to anend, the integrating circuit 40 starts with its integrating operation.Thus, a slowly increasing voltage is generated by the integratingcircuit 40. If no yarn breakage occurs, the integrating circuit becomesreset as soon as the derivator 32 generates a positive gradient signal.Within this time, the output voltage of the integrating circuit 40 doesnot exceed the voltage threshold of the comparator 34. If, on thecontrary, a yarn breakage occurs, no positive gradient signal will begenerated by the derivator 32. Thus, the integrating circuit generates acontinuously increasing output voltage (until this voltage equals thesupply voltage of the integrating circuit 40). In this case, thethreshold comparator 34 generates a high logical potential output signalsetting the circuit 35 and opening the relay 36. Thus, the loom isstopped in case of a yarn breakage.

FIG. 10 shows a circuit diagram of the fourth embodiment of theinventive loom control system. The low pass filter 31 consists of aresistor R₁₀ and a capacitor C₁₀ in serial connection. The common nodeof these elements R₁₀, C₁₀ is connected to the input terminal of thederivator 32. This derivator comprises a capacitor C₁₁ connected to itsinput terminal and the negative input terminal of an operationalamplifier OP₁₀. The positive terminal of this amplifier is grounded. Aresistor R₁₁ is connected to the negative input terminal and to theoutput terminal of this amplifier and serves as a feedback-path. Theoutput signal of this circuitry OP₁₀, C₁₁, R₁₁ is the negative firstderivation of its input signal. The derivator 32 also comprises invertercircuitry R₁₂, R₁₃, OP₁₁ similar to the inverter 22 of FIGS. 5 and 6.This inverter circuit changes the sign of the output signal of amplifierOP₁₀. Thus, the output signal of the derivator 32 corresponds to thegradient of the sensor signal. Said gradient signal is fed to a firstinput terminal of the OR-gate 46, wherein the second input terminal ofthis gate is connectable to a DC-source by means of a switch whichserves as digital weft yarn insertion sensor 45. This switch is operatedby the weft yarn insertion means.

The output signal of the OR-gate is fed to the positive input terminalof an operation amplifier OP₁₂, which serves as an impedancetransformer. The output signal of this amplifier OP₁₂ is a reset signalfor the integrating circuit 40. The integrating circuit 40, thethreshold comparator 35, the RS-flip-flop circuit 35 and the relay 36are quite similar to the circuit elements 23 to 26 of FIG. 6, so that itis believed that a detailed explanation of these elements can beomitted.

The embodiments of FIGS. 5 to 10 are capable of detecting a yarnbreakage between the supply spool S and the feeding device 1. However, ayarn breakage might even occur between the feeding device 1 and theloom. The fifth embodiment (FIG. 11) of the loom control system inaccordance with the present invention is capable of detecting this kindof yarn breakage. This embodiment comprises an analog yarn sensor 30, alow pass filter 31, a derivator 32, a digital weft yarn insertion sensor45, an AND-gate 46, a RS-flip-flop circuit 35 and a relay 36.

If no yarn breakage occurs, the quantity of yarn stored on the drumdecreases during weft yarn insertion. Only if the yarn breaks betweenthe feeding device 1 and the loom, the quantity of yarn increasesalthough a weft yarn insertion signal is generated by the sensor 45.Therefore, the simultaneous occurence of a positive gradient of thequantity of yarn with respect to time and a weft yarn insertion signalrepresenting that weft yarn insertion has taken place indicates thatthis kind of yarn breakage has occured. The embodiment of FIG. 11includes an AND-gate 46 for determining whether the above mentionedcondition is fulfilled. If so, the AND-gate 46 generates a high signalfor setting the circuit 35, which in turn opens the normally closedpower switch of relay 36. Thus, the loom is stopped by the loom controlsystem as shown in FIG. 11 in case of a yarn breakage between the drumand the loom.

It is evident for a man skilled in the art that the circuitries as shownin FIGS. 5 to 11 can easily be combined with each other so as to providea loom control system capable of detecting more than only one possibleerror-condition. For example, it is possible to use a commonRS-flip-flop circuit 25, 35 and a common relay 26, 36 for a loom controlsystem comprising more than one of said embodiments. In this case, theoutput signals of the respective circuit elements, which are shown asbeing connected to the respective RS-flip-flop circuits 25, 35 are usedas input signals to an OR-gate connected to the set-terminal of thecommon RS-flip-flop circuit.

It is also easily possible for a man skilled in the art to replace theembodiments shown in FIGS. 5 to 11 by a suitably programmedmicro-processor.

Furthermore, the above described opto-electric sensors can be replacedby mechanical sensors.

The control system in accordance with the present invention can also beapplied to each kind of thread processing machines comprising a feedingdevice for generating a substantially constant tension of the yarn to befed to the processing machine. Thread processing machines comprisingfeeding devices can be, for example, winding machines for re-spoolingthe yarn from one spool to another, twisting machines, spinning machinesand knitting machines. Furthermore, the control system in accordancewith the present invention can also be applied to winding machines forwinding an electrical conductor on the core of a rotor of an electricalmotor, and for winding an electrical conductor on a core of anelectrical coil.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A loom control systemoperable to stop a loom in the presence of a yarn breakage, said loomincluding a feeding device having a yarn storage drum for temporarilystoring the yarn, and yarn store sensor means for sensing the quantityof yarn stored on said drum of said feeding device and for transmittingan electric sensor signal representing the quantity of yarn stored onsaid drum to said feeding device to control the operation of saidfeeding device and to thereby control the quantity of yarn stored onsaid drum, said loom control system including monitor means fordetecting a yarn breakage and for stopping the loom in the event of ayarn breakage, wherein the improvement comprises said monitor meansbeing electrically connected to said yarn store sensor means forreceiving said sensor signal therefrom, and said monitor means beingresponsive to said sensor signal representing the quantity of yarnstored on said drum for detecting a yarn breakage and said monitor meansgenerating a stop signal for the loom in response to detection of a yarnbreakage.
 2. Loom control system as claimed in claim 1, wherein saidsensor signal generated by said yarn store sensor means indicateswhether the quantity of stored yarn is below a minimum threshold,wherein said monitor means is responsive to the period of time duringwhich said sensor signal indicates that the quantity of stored yarn iscontinuously below said minimum threshold, and wherein said monitormeans stops the loom if said period of time exceeds a predetermined timethreshold.
 3. Loom control system as claimed in claim 1, wherein saidfeeding device is controlled so as to essentially continuously feed theyarn to said drum, wherein said yarn store sensor means includes ananalog sensor, wherein said sensor signal is proportional to thequantity of yarn stored on said drum, wherein said monitor meansgenerates a gradient signal representing the first derivative of saidsensor signal with respect to time, wherein when said gradient signal isnegative, which indicates a decreasing quantity of yarn stored on saiddrum, said monitor means compares the absolute value of the negativegradient signal with a predetermined gradient threshold, and whereinsaid monitor means stops the loom if said absolute value exceeds saidgradient threshold.
 4. Loom control system as claimed in claim 1,wherein said yarn store sensor means includes an analog sensor, whereinsaid sensor signal is proportional to the quantity of yarn stored onsaid drum, wherein said monitor means generates a gradient signalrepresenting the first derivative of said sensor signal with respect totime, wherein said monitor means measures the period of time duringwhich said gradient is continuously negative, and wherein said monitormeans stops the loom if said period of time exceeds a predetermined timethreshold.
 5. Loom control system as claimed in claim 1, wherein saidfeeding device is controlled so as to essentially continuously feed theyarn to said drum, wherein said yarn store sensor means includes ananalog sensor, wherein said sensor signal is proportional to thequantity of yarn stored on said drum, wherein said monitor meansgenerates a gradient signal representing the first derivative of saidsensor signal with respect to time, wherein said loom control systemincludes insertion sensor means for generating a yarn insertion signalwhen a weft yarn insertion takes place, wherein when said gradientsignal is a negative gradient signal said monitor means is responsive tothe period of time during which said insertion signal indicates that noweft yarn insertion takes place, and wherein said monitor means stopsthe loom if, while said gradient signal is negative, said period of timeexceeds a predetermined time threshold.
 6. Loom control system asclaimed in claim 1, wherein said feeding device is controlled so as toessentially continuously feed the yarn to said drum, wherein said yarnstore sensor means includes an analog sensor, wherein said sensor signalis proportional to the quantity of yarn stored on said drum, whereinsaid monitor means generates a gradient signal representing the firstderivative of said sensor signal with respect to time, wherein said loomcontrol system includes insertion sensor means for generating a yarninsertion signal when a weft yarn insertion takes place, and whereinsaid monitor means stops the loom if the following two conditions aresimultaneously fulfilled:(a) said gradient signal is positive, and (b)said insertion signal is indicating the occurrence of a weft yarninsertion.